Apparatus and method for writing data to a magnetic recording medium in the form of magnetization vectors having alternating magnetic orientations and lengths ranging from a minimum symbol length to a maximum symbol length. A write element adjacent the medium includes a leading edge and a trailing edge to form a write gap which generates a write gap recording field having a length substantially greater than the minimum symbol length. A write driver applies a write current signal to the write element as a series of current pulses, each pulse magnetizing an area of the disc corresponding to the length of the write gap recording field. A subsequent current pulse is applied while a portion of a first area magnetized by a previous pulse remains disposed between the leading edge and the trailing edge of the write element, so that the remaining portion of the first area beyond the trailing edge of the write element forms a magnetization vector of selected symbol length.
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10. A data storage device, comprising:
a recording medium to which data are magnetically stored as a sequence of magnetization vectors having alternating magnetic orientation and associated lengths that range from a minimum symbol length to a maximum symbol length; a write element, adjacent the recording medium, having a leading edge and a trailing edge to form a write gap which generates a write gap recording field having a length that exceeds the maximum symbol length; and means for writing data to the recording medium by applying write signals to the write element as a series of current pulses of short duration with respect to a period of time required for a point on the disc to traverse the write gap, wherein different elapsed times between successive current pulses are used to write magnetization vectors having correspondingly different symbol lengths.
12. A method for recording data using a data transducing head having a write gap and a magnetic recording medium having a recording surface, the head providing a write gap recording field which selectively magnetizes the recording surface along a length substantially equal to a length of the write gap, the data recorded as a sequence of magnetization vectors having alternating magnetic orientation and associated symbol lengths that range from a minimum symbol length to a maximum symbol length, the method comprising applying a sequence of electrical pulses of short time duration to the head, wherein the time duration of each pulse is a small fraction of a traverse time defined as an elapsed time for a point on the recording surface to traverse the length of the write gap, and wherein an elapsed time period between each pair of successive pulses varies for different symbol lengths and is selected independently of the traverse time.
6. A disc drive, comprising:
a rotatable disc to which data are magnetically stored as a sequence of magnetization vectors having alternating magnetic orientation and associated lengths that range from a minimum symbol length to a maximum symbol length; a write element, adjacent the disc, having a leading edge and a trailing edge to form a write gap which generates a write gap recording field having a length substantially greater than the minimum symbol length; and a write driver, connected to the write element, which writes input data to the disc as a series of current pulses of short duration with respect to a period of time required for a point on the disc to traverse the write gap, wherein each current pulse magnetizes an area of the disc corresponding to the length of the write gap recording field, each area having a magnetic orientation determined by a polarity of the associated current pulse, and wherein a subsequent current pulse is applied while a portion of an area magnetized by a previous pulse remains disposed between the leading edge and the trailing edge of the write element so that the portion is magnetically reoriented by the subsequent current pulse, a remaining portion of the area magnetized by the previous pulse disposed beyond the trailing edge of the write element comprising a selected magnetization vector of selected symbol length, wherein different elapsed periods of time between the first and second pulses are used to provide different symbol lengths for the selected magnetization vector.
1. A method for magnetically recording input data to a magnetic medium as a sequence of magnetization vectors having alternating magnetic orientation and associated lengths that range from a minimum symbol length to a maximum symbol length, the method comprising steps of:
providing a write element having a leading edge and a trailing edge to form a write gap which generates a write gap recording field having a length substantially greater than the minimum symbol length; applying a first current pulse to the write element to magnetically orient a first area of the magnetic medium in a first direction; and subsequently applying a second current pulse to the write element to magnetically orient a second area of the magnetic medium in a second direction opposite the first direction, the first and second current pulses of opposite polarity and each having a substantially short duration with respect to a period of time required for a point on the magnetic medium to traverse the write gap, wherein the second current pulse is applied while a portion of the first area remains between the leading edge and the trailing edge of the write element so that the portion of the first area is magnetically reoriented by the second current pulse, a remaining portion of the first area beyond the trailing edge of the write element comprising a selected magnetization vector of desired symbol length, wherein the elapsed period of time between the first and second pulses is variably adjusted in relation to the desired symbol length of the selected magnetization vector.
2. The method of
3. The method of
(d) subsequently applying a third current pulse to the write element to magnetically orient a third area of the magnetic medium in the second direction so that the second and third areas form a second magnetization vector with the maximum symbol length.
5. The method of
(d) dividing the disc radially into a plurality of zones each comprising a plurality of tracks to which the data are written at a common write frequency, wherein at least one zone has a highest write frequency and at least one zone has a lowest write frequency; (e) evaluating each zone to determine whether the associated write frequency is sufficiently high to cause the length of the write gap recording field to exceed the maximum symbol length for magnetization vectors written to the zone; and (f) for each zone wherein the length of the write gap recording field does not exceed the maximum symbol length for magnetization vectors written to the zone, subsequently applying a third current pulse to the write element to magnetically orient a third area of the magnetic medium in the second direction so that the second and third areas form a second magnetization vector with a symbol length that exceeds the length of the write gap recording field.
7. The disc drive of
8. The disc drive of
9. The disc drive of
11. The data storage device of
13. The method of
14. The method of
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This application claims priority to United States Provisional Application No. 60/121,031 filed Feb. 22, 1999.
This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to improving data transfer rate performance by writing data to a magnetic medium using discrete pulsed write currents.
Disc drives are used as primary data storage devices in modern computer systems and networks. A typical disc drive comprises one or more rigid magnetic storage discs which are journaled about a spindle motor for rotation at a constant high speed. An array of read/write transducing heads are provided to transfer data between tracks of the discs and a host computer in which the disc drive is mounted. The heads are mounted to a rotary actuator assembly and are controllably positioned adjacent the tracks by a closed loop servo system.
Each of the disc surfaces is provided with a magnetizable media coating to retain the data as a series of magnetic domains of selected orientation which are impressed by a write element of the corresponding head and subsequently detected by a read element of the head. Although a variety of head constructions have been utilized historically, magneto-resistive (MR) heads are typically used in disc drives of the present generation. An MR head uses a thin-film inductive coil arranged about a ferromagnetic core with a write gap so that, as write currents are passed through the coil, magnetic flux lines fringing across the write gap extend into the adjacent media to establish magnetization vectors, or intervals, in directions along the track. Magnetic flux transitions are established at boundaries between adjacent intervals of opposite orientation, and these flux transitions (each indicative of a logical one) are detected by an MR read element which has a characteristic electrical resistance that changes in the presence of a magnetic field. Thus, by passing a small biasing current through the MR read element, the flux transitions can be transduced in relation to the voltage across the MR read element.
To write a computer file to disc, a disc drive receives the file from the host computer in the form of input data which are buffered by an interface circuit. A write channel encodes and serializes the data to generate a data stream that can be represented as a square-wave type signal with varying interval (symbol) lengths between successively occurring rising and falling edges. The placement of the rising and falling edges correspond to the logical ones in the data sequence.
A preamplifier/driver circuit (preamp) uses the data stream to generate write currents which are applied to the head to write the encoded data to the selected disc surface. Typically, disc drives use a continuous write current that toggles from a maximum current value of a first polarity (such as +50 milliamps, mA) to a corresponding maximum current value of a second, opposite polarity (such as -50 mA), with the periodic changes in current direction inducing the aforementioned flux transitions on the media. Such methodology is discussed, for example, in U.S. Pat. No. 5,159,501 issued Oct. 27, 1992 to Genheimer.
While constant current recording has been found useful, it becomes increasingly difficult to write the data using a continuous current at higher transfer rates such as greater than one gigabit (Gb) per second (1×109 bits/sec), due to various factors including stray inductance and capacitance along the conductive paths between the heads and the preamp, the slew rate in the positive and negative transitions, and the power dissipated by the preamp.
As an alternative to a continuous write current, impulse magnetic recording has been proposed in the prior art as discussed by U.S. Pat. No. 4,562,491 issued Dec. 31, 1985 to Kawabata et al. and U.S. Pat. No. 4,965,873 issued Oct. 23, 1990 to White. Kawabata et al. proposes writing data to a magnetic medium by converting each continuous current pulse into a series of very short duration, discrete pulses for each interval. By time shifting the pulses supplied to a number of different heads, data can be written to multiple heads at the same time using a single power supply with a current output capacity sufficient for only one head. White also proposes writing data using a series of positive and negative transition pulses of very short duration. White uses higher amplitude transition pulses to write flux transitions and uses additional, lower amplitude sustaining pulses of the same polarity to sustain the recorded magnetic field for longer intervals between successive transition pulses. It will be noted that both Kawabata et al. and White are directed to relatively lower data transfer rates and use multiple current pulses to write the magnetization vectors.
While operable, there remains a continued need for improvements in the art to enhance magnetic write performance at ever increasing data transfer rates. It is to this end that the present invention is directed.
The present invention provides an apparatus and method for improving disc drive data transfer rate performance.
In accordance with preferred embodiments, a disc drive comprises a rotatable disc to which data are stored as a sequence of magnetization vectors having alternating magnetic orientation and associated lengths that range from a minimum symbol length (such as 1T) to a maximum symbol length (such as 6T).
A write element is provided having a leading edge and a trailing edge to form a write gap therebetween, the write gap generating a write gap recording field having a length substantially greater than the minimum symbol length. A first current pulse is applied to the write element to magnetically orient a first area of the magnetic medium in a first direction. A second current pulse is subsequently applied to the write element to magnetically orient a second area of the magnetic medium in a second direction opposite the first direction. The first and second current pulses have opposing polarities and respective short durations with respect to a period of time required for a point on the magnetic medium to traverse the write gap.
The second current pulse is applied while a portion of the first area remains between the leading edge and the trailing edge of the write element so that the portion of the first area is magnetically reoriented by the second current pulse. The remaining portion of the first area disposed beyond the trailing edge of the write element comprises a magnetization vector of desired symbol length.
In one preferred embodiment, the length of the write gap recording field exceeds the maximum symbol length. In such case, the application of each current pulse is sufficient to magnetize the medium for all symbol lengths. In another preferred embodiment, the length of the write gap recording field remains substantially greater than the minimum symbol length, but is less than the maximum symbol length. In such case, an additional extension pulse is applied having the same polarity as the immediately preceding pulse to form a magnetization vector having a symbol length greater than the length of the write gap recording field.
These and various other features and advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.
Referring to
A spindle motor 106 rotates a plurality of magnetic recording discs 108 at a constant high speed (in thousands of revolutions per minute) in an angular direction denoted by arrow 109. User data are written to and read from tracks (not designated) on the discs 108 through the use of an actuator assembly 110, which rotates about a bearing shaft assembly 112 adjacent the discs 108. The actuator assembly 110 includes a plurality of rigid actuator arms 114 which support flexible suspension assemblies 116 (flexures). A head 118 is supported at the end of each flexure 116, with the heads preferably having a magneto-resistive (MR) construction.
When the disc drive 100 is not in use, the heads 118 are parked on landing zones 120 and the actuator assembly 110 is secured using a magnetic latch assembly 122. A voice coil motor (VCM) 124 controls the position of the heads 118 through application of current to a coil 126 which interacts with a magnetic circuit which includes a permanent magnet 128. A flex assembly 130 facilitates electrical communication between the actuator assembly 110 and a disc drive printed circuit board (PCB) mounted to the underside of the base deck 102. The flex assembly 130 includes a preamplifier/ driver circuit 132 (preamp) which electrically interfaces with the heads.
To readback previously stored data, a detection amplifier 142 of the preamp 132 applies a read bias current to a magneto-resistive (MR) read element 144 and transduces the selective magnetization of the disc 108 to form a readback signal in relation to changes in voltage across the read element 144. The detection amplifier 142 further amplifies and conditions the readback signal and supplies the same to a read channel 146 of the data channel 134 to reconstruct the output data.
The write element 140 includes a generally horseshoe-shaped ferromagnetic core 152 about which a conductor 154 is wound to form a coil 156. When write currents lw are passed along the conductor 154, magnetic flux lines are established in the core 152 and traverse a write gap 158, generating a write gap recording field (WGRF) 160 of sufficient strength to magnetically orient the enveloped portion of the layer 148, as shown.
Write currents in a first direction serve to magnetically orient the layer 148 along the track in the direction represented by magnetization vector 162, which is the same as the direction of rotation 109 of the layer 148; write currents in a second, opposite direction orient the layer 148 in the opposite direction along the track. The core 152 includes a leading edge (LE) 164 and a trailing edge (TE) 166 with the write gap 158 formed in the space therebetween. The WGRF 160, also referred to as a magnetic bubble, has a length along the track that is determined by, and slightly exceeds, the distance between the LE 164 and the TE 166 (i.e., the "width" of the write gap 158). It will be readily understood that the magnetic field generated by the write gap does not abruptly stop beyond the bubble 160, but rather, the bubble generally represents the extent to which the magnetization of the layer 148 has sufficient field strength to be subsequently recovered by the read element 144. Reversals in magnetization (flux transitions) are nominally generated at locations defined at the trailing edge of the WGRF 160.
For reference,
While advantageously writing the data stream to the media 148, the prior art methodology of
Accordingly,
For the example of
In the example of
First, at time t0, the current pulse 226 of
At time t1, the second current pulse 228 of
It can be seen that the area 236 overlaps the area 234 by an increment 238, since the second pulse 228 is applied before all of the area 234 previously magnetized at time to passes the write gap 158. Thus, the subsequently applied pulse 228 "trims" the area previously magnetized by the pulse 226 to produce the desired symbol length (3T in this case).
Continuing with
Finally, the current pulse 232 is applied at time t3 to magnetize an area 244 with the same magnetic orientation as at time t1. The area 244 defines the magnetic flux transition 170 and overlaps the previously magnetized area 240 by an increment 246, resulting in the 1T interval as shown.
It will be noted that the length of the media layer 148 that is trimmed upon the occurrence of each successive current pulse is equal to the difference in length between the WGRF 160 and the resulting symbol length. Thus, every area that is magnetized in response to a current pulse (such as the areas 234, 236, 240 and 244) has at least a portion thereof that undergoes two successive magnetizations in opposite directions (such as indicated by the increments 238, 242 and 246).
It follows that, depending upon the relative geometries between the WGRF 160 and the minimum symbol length, a portion of an area magnetized by a current pulse might undergo any number of magnetization changes as it passes between the leading and trailing edges of the WGRF 160 in relation to the ratio between WGRF and symbol length. For example, if a series of 1T symbols are written in succession, and the WGRF is about 6T in length, the portion of the media layer 148 immediately adjacent the leading edge of the WGRF established by the first current pulse will be alternately magnetized a total of six times before emerging as a 1T symbol.
The write current signal 250 of
At time t1, the current pulse 258 magnetizes an area 268 in a second direction. The trailing edge of the area 268 defines the flux transition 174. The area 268 further overlaps the previously magnetized area 266 by an increment 270.
At time t2, the current pulse 260 is applied to magnetize an area 272 with the same magnetization as the area 268. In this example, the current pulse 260 is applied just as an edge 274 of the area 268 (at time t1) passes the trailing edge 166 of the write element 140 (at time t2). Of course, in alternative embodiments the current pulse 260 can occur in a shorter interval of time after the current pulse 258 to cause the adjacent, same orientation magnetization areas 268, 272 to overlap slightly, as desired. The current pulse 260 thus operates as an extension pulse to extend the area of magnetization of the magnetic layer to a length longer than the length of the WGRF 160.
Continuing with
It will be noted that disc drives typically record data on a zone basis, so that different zones or groups of tracks across the disc surfaces have data written at different frequencies, with higher write frequencies at tracks disposed near outer radii of the discs and lower write frequencies at tracks disposed near inner radii of the discs. It is contemplated that, as areal recording densities increase, even at the lowest data recording frequency the WGRF 160 will exceed the maximum symbol length so that the methodology as set forth by the write current signal 220 in
The opposite case, of course, is that even the highest data recording frequency still results in a WGRF 160 that is greater than the minimum symbol length, but less than the maximum symbol length. In this case, the methodology of
A third possibility is that the maximum data recording frequency (at outer disc radii, for example) results in symbol lengths that are less than the WGRF 160, but the minimum data recording frequency (at inner disc radii, for example) provides symbol lengths that are greater than the WGRF 160. In this case, the disc drive could write test patterns by zone of tracks and determine whether the methodology of
At step 302, the disc drive 100 is first configured with a write gap recording field (such as the WGRF 160 in
Next, at decision step 306, the routine determines whether the write gap recording field (WGRF) has a length that is greater than the length of the maximum symbol length (maxT). If not, provision is made for additional, extension pulses (such as the extension pulse 260 of
The present invention, as embodied hereinabove and claimed below, provides several advantages over the prior art. First, the use of current pulses significantly reduces the power requirements for the write driver 138 as compared to continuous write current methodologies such as discussed in FIG. 6. Better edge definition and control can also be obtained, as well as faster switching since the write driver only needs to switch between 0 amps and the positive and negative maximum current amplitudes, instead of switching between maximum current amplitude extremes.
Although preferred embodiments disclosed herein have contemplated the use of a rotatable disc, it will be apparent that the claimed invention can be readily used with other types of magnetic media, such as magnetic tape.
In summary, it will be recognized that the present invention is directed to an apparatus and method for writing data to a magnetic medium. In accordance with preferred embodiments, the magnetic medium comprises a disc 108 of a disc drive 100. The data are stored as a sequence of magnetization vectors 162, 180, 182, 184 having alternating magnetic orientation and associated lengths that range from a minimum symbol length (such as 1T) to a maximum symbol length (such as 6T).
A write element 140 is provided having a leading edge 164 and a trailing edge 166 to form a write gap 158 which generates a write gap recording field 160 having a length substantially greater than the minimum symbol length. A first current pulse 226, 256 is applied to the write element 140 to magnetically orient a first area 234, 266 of the magnetic medium in a first direction. A second current pulse 228, 258 is subsequently applied to the write element 140 to magnetically orient a second area 268 of the magnetic medium in a second direction opposite the first direction. The first and second current pulses have opposing polarities and respective short durations with respect to a period of time required for a point on the magnetic medium to traverse the write gap 158.
The second current pulse is applied while a portion 238, 270 of the first area remains between the leading edge 164 and the trailing edge 166 of the write element 140 so that the portion of the first area is magnetically reoriented by the second current pulse. The remaining portion of the first area disposed beyond the trailing edge of the write element comprises a magnetization vector 184 of desired symbol length.
In one preferred embodiment, the length of the write gap recording field exceeds the maximum symbol length. In such case, the application of each current pulse is sufficient to magnetize the medium for all symbol lengths. In another preferred embodiment, the length of the write gap recording field remains substantially greater than the minimum symbol length, but is less than the maximum symbol length. In such case, an additional extension pulse is applied having the same polarity as the immediately preceding pulse to form a magnetization vector having a symbol length greater than the length of the write gap recording field.
It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.
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